The use of renewable biological material for the production of biofuels is generally motivated by decreasing climate change impacts, by securing the supply of fuels and by economic factors. However, the use of edible crops to create fuels instead of further refining them to food for increasing human population is more and more ethically short-lived. Therefore, biological sources that cannot be used for feeding of people or cattle and that can be manufactured in environmentally friendly manner, are of growing interest.
BCC Research estimates that the global market for liquid biofuels was worth $30.3 billion in 2008. This should increase to $42.8 billion in 2013, for a compound annual growth rate (CAGR) of 7.2 Another perspective to the market is the volume. In 2008 biofuel production capacity across the 21 countries considered in the study report of European Union totalled 10.9 billion liters of biodiesel, and 66.6 billion liters of bioethanol. Over 99% of this production is considered as so called 1st generation biofuel, including both sugar and starch based bioethanol, and oilseed and waste oil based biodiesel. Biodiesel can be made from oilseed crops, animal fats or from recycled greases. Since it is known that algae and sonic microorganisms are capable of producing and/or accumulating lipids, also their use as the source of oil for biodiesel has been suggested. These microorganism based oils are often called as single cell oils. Campbell 2008 and Strobel et al., 2008 have described optimization of the cultivation conditions of algae and fungi in different type of bioreactors to maximize the yields of lipids and fatty acids for refining of biofuels.
Alternative option to photosynthetic production of lipids is to utilize heterotrophic organisms which produce lipids from organic molecules (such as sugars) without need for light. Single cell oil production process using heterotrophic microorganisms comprises cultivating microorganisms in aerated bioreactors, allowing cells to accumulate lipids, harvesting lipid-rich cells and recovering oil from cells (Ratledge et al., 2005, Meng et al., 2009).
Single-cell oils have traditionally been used as special products e.g. in health foods, not as commodity chemicals. In these kinds of single cell oil production processes product volumes are relatively small and the product is expensive. Therefore, the cost structure of these processes allows the utilization of expensive feed raw materials and unit operations. Similar kind of production process has also been described for the production of lipids for biodiesel production (Ratledge and Cohen 2008; Meng et al. 2009). However, as the product is an inexpensive commodity chemical, the process costs should not be on the level of the process costs of special products. Further, the lipid yield by heterotrophic microorganisms is typically very low, less than 20% weight percent of the fed sugar (Ratledge and Cohen, 2008).
Less expensive raw materials for use in lipid production by heterotrophic microorganisms have been suggested in some recent patent publications. WO 2009/034217 A1 has described a fermentation method to make paraffins, fatty acids and alcohols by waste materials and microbes. WO 2009/046375 A2 suggests the conversion of polysaccharides derived from biomass into monosaccharides, or oligosaccharides and converting them into biofuels by using recombinant microorganisms comprising exogenous genes that allow the microorganism to grow on the polysaccharide as a sole source of carbon. US 2009/0064567 A1 discloses the production of biological oils by heterotrophic fermentation by growing microorganism of the kingdom Stramenophile by using cellulose-containing feedstock as a main source of carbon. WO2009/011480 A1 discloses the production of biological oils from depolymerised cellulosic material by microalgae and fungi. US 2009/0148918 A1 discloses a method of lipid manufacturing by culturing a microalgae on glycerol as a source of carbon. In addition WO 2009/009391 A2 discloses the production of fatty esters by first producing an alcohol composition and providing it into a fatty ester production host. WO 2009/063138 describes a method for treating organic material with water, acid or alkali and grinding. A precipitate and filtrate are separated and used for lipid production in a cultivation medium for a lipid producing microorganism.
Since the economy of the production of single cell oils for biofuels is of key importance, new cost-effective processes for lipid production for biofuel production are still of growing interest.